JIS S43C is a medium-carbon machine structural steel defined under JIS G4051, with a carbon content of 0.40–0.46%. It bridges the gap between S40C and S45C, offering induction hardening capability approaching S45C (HRC 54–60) while retaining marginally better weldability than S45C. It is used for shafts, spindles, connecting rods, and keys where a precise balance of strength and hardness is required. Internationally it aligns with AISI 1043 (USA) and is close to DIN C45 (Germany).
- International Equivalent Grades
- Chemical Composition
- Mechanical Properties
- Physical Properties
- Heat Treatment Conditions
- Machinability
- Weldability
- Common Mistakes
- When to Choose S43C
- FAQ
1. International Equivalent Grades
| Standard | Grade | Region | Match Type |
|---|---|---|---|
| JIS G4051 | S43C | Japan | Reference |
| ASTM / AISI | 1043 | USA | ✅ Exact Match |
| ISO 683-1 | C45 | International | ⚠️ Nearest Equivalent |
| DIN | C45 / 1.0503 | Germany | ⚠️ Nearest Equivalent |
| EN | C45E / 1.1191 | Europe | ⚠️ Nearest Equivalent |
2. Chemical Composition
| Element | JIS S43C | AISI 1043 | DIN C45 |
|---|---|---|---|
| C | 0.40–0.46% | 0.40–0.47% | 0.42–0.50% |
| Si | 0.15–0.35% | 0.10–0.35% | ≤ 0.40% |
| Mn | 0.60–0.90% | 0.60–0.90% | 0.50–0.80% |
| P | ≤ 0.030% | ≤ 0.040% | ≤ 0.045% |
| S | ≤ 0.035% | ≤ 0.050% | ≤ 0.045% |
Sources: JIS G4051:2016, ASTM A29/A29M, DIN EN 10083-2
3. Mechanical Properties
As-normalized
| Property | Value (Metric) | Value (Imperial) |
|---|---|---|
| Tensile Strength | ≥ 600 MPa | ≥ 87.0 ksi |
| Yield Point | ≥ 355 MPa | ≥ 51.5 ksi |
| Elongation (GL=5d) | ≥ 15% | ≥ 15% |
| Reduction of Area | ≥ 40% | ≥ 40% |
| Hardness | 170–241 HB | 170–241 HB |
Induction hardening (surface, sections ≤ 30 mm / 1.2 in)
| Property | Value |
|---|---|
| Surface hardness | HRC 54–60 |
| Effective case depth | 1.0–3.0 mm (0.039–0.118 in) |
After through-hardening + temper (sections ≤ 25 mm / 1 in)
| Temper Temperature | Tensile Strength | Hardness |
|---|---|---|
| 400°C (752°F) | ~950–1050 MPa (138–152 ksi) | HRC 35–42 |
| 550°C (1022°F) | ~750–850 MPa (109–123 ksi) | HRC 24–32 |
| 650°C (1202°F) | ~600–700 MPa (87–101 ksi) | HRC 18–25 |
4. Physical Properties
| Property | Value (Metric) | Value (Imperial) |
|---|---|---|
| Density | 7.85 g/cm³ | 0.284 lb/in³ |
| Young’s Modulus | 206 GPa | 29,900 ksi |
| Thermal Conductivity | 50 W/(m·K) | 347 BTU·in/(hr·ft²·°F) |
| Thermal Expansion (20–100°C / 68–212°F) | 11.3 × 10⁻⁶ /°C | 6.3 × 10⁻⁶ /°F |
| Specific Heat | ~486 J/(kg·K) | 0.116 BTU/(lb·°F) |
5. Heat Treatment Conditions
| Process | Temperature | Cooling | Purpose |
|---|---|---|---|
| Normalizing | 840–870°C (1544–1598°F) | Air cool | Refine grain, relieve stress |
| Annealing | 810–850°C (1490–1562°F) | Furnace cool | Soften for machining |
| Through-Hardening (quench) | 820–860°C (1508–1580°F) | Water or oil quench | Full-section hardening |
| Tempering | 400–650°C (752–1202°F) | Air cool | Adjust strength / toughness balance |
| Induction Hardening | 860–920°C surface (1580–1688°F) | Water or oil quench | Surface hardening HRC 54–60 |
6. Machinability
- Machinability rating: approximately 55–60% relative to AISI 1212 baseline (100%)
- Normalized or annealed condition recommended for rough and finish machining
- Carbide tooling preferred for production runs
- Induction-hardened surface finishing requires grinding
7. Weldability
S43C is in the upper range of conditionally weldable carbon steels. Treat welding procedure similarly to S45C.
- Preheat: 100–150°C (212–302°F) for sections over 15 mm (0.6 in); strongly recommended for all restrained joints
- Process: Low-hydrogen consumables essential (E7018 for SMAW, ER70S-6 for GMAW)
- Post-weld: Stress relief at 550–600°C (1022–1112°F) recommended
8. Common Mistakes
The 0.03% additional carbon in S43C over S40C meaningfully raises the Ceq and increases HAZ hardening tendency. Engineers who apply S40C welding procedures (lower preheat or no preheat) to S43C risk cold cracking, particularly in restrained joints or cold-weather fabrication.
S43C is not as widely stocked as S40C or S45C. For standard applications, one of the two neighbouring grades is almost always available and equally suitable. Reserve S43C for cases where the design specifically targets its intermediate property range and stock availability has been confirmed.
9. When to Choose S43C
- ✅ Shafts and spindles requiring induction hardness HRC 54–60 with moderate core toughness
- ✅ Connecting rods and keys where normalized tensile strength of 600+ MPa is needed
- ✅ Applications where S40C is slightly under-strength and S45C introduces more weldability constraint than necessary
- ✅ Direct replacement for AISI 1043 in North American-designed components being manufactured in Japan
- ❌ Maximum induction hardness (HRC 58–62) required — use S45C or S50C
- ❌ Easy field welding without preheat — use S35C or structural grades
- ❌ Applications where stock availability is critical — confirm supply before specifying
10. FAQ
Q: Is S43C the same as AISI 1043?
Yes, for practical purposes. Carbon and manganese ranges are virtually identical. JIS G4051 applies tighter P and S limits, making S43C marginally cleaner. The two grades are directly interchangeable in shafting, induction hardening, and through-hardening applications.
Q: Is DIN C45 a good substitute for S43C?
Close, but not exact. DIN C45 (C: 0.42–0.50%) allows higher carbon than S43C (0.40–0.46%), which can result in slightly higher as-quenched hardness and marginally lower toughness. For most applications these differences are inconsequential. Verify actual mill chemistry when precision heat treatment response is specified.
Q: Why choose S43C over S45C?
Primarily for welding reasons. S43C’s lower carbon ceiling (0.46% vs. S45C’s 0.48%) gives a marginally lower Ceq, reducing — but not eliminating — preheat requirements in some joint configurations. The practical difference is small; if welding is a major design concern, S35C or SM490 are more impactful choices.
Q: What induction hardness does S43C achieve compared to S45C?
S43C typically achieves HRC 54–60, compared to S45C’s HRC 55–62. The difference of 1–2 HRC is small and within heat-to-heat variability. Both grades are suitable for standard induction hardening specifications calling for HRC 54 minimum.
Q: Is S43C available outside Japan?
AISI 1043 is the direct equivalent and is available from US and some European bar steel suppliers. DIN C45 / EN C45E covers most of the same compositional space and is widely available in Europe. Outside Japan, specify 1043 (ASTM) or C45 (DIN/EN) and cross-reference to S43C for traceability.
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